1. Field of the Invention
This invention relates to a self-hardenable material. More particularly it relates to a self-hardenable material forming a fluoro-apatite type product and useful for example as materials for substitutes or fillers of living body.
2. Description of Related Art
Calcium-phosphorus apatite as a kind of calcium phosphates (hereinafter referred to merely as apatite) is expressed by a theoretical formula Ca.sub.10 (PO.sub.4).sub.6 X.sub.2 (wherein X represents an anion such as OH.sup.-1, Cl.sup.-1, F.sup.-, etc.) Here, the g.cndot.atom ratio of Ca/P is theoretically 10/6=1.67, but it has been regarded that practically the apatite structure can be formed in a Ca/P ratio in the range of 1.3 to 2.0.
Thus, various general formulas have been proposed, and for example, Ca.sub.10-y (HPO.sub.4).sub.y (PO.sub.4).sub.6-y X.sub.2-y is illustrated, wherein X is as defined above and y is a number of 0 to 2.
This apatite is a main component of mineral ones of teeth or bones and so superior in the affinity in vivo that it easily assimilates with the tissues of living body; hence its utilization as a tooth implant or a filler for bone defect part has been energetically studied. However, in spite of the excellent affinity of the apatite with living body, it is the present due to the following reason status that its utilization as materials for living body such as dental materials, medical materials, etc. has been very small.
Heretofore, as to the utilization of the apatite as materials for living body, there has been mainly employed a method of molding hydroxyapatite powder according to press molding, cast molding or the like molding, followed by calcining the resulting material into ceramics to obtain a desired molded product. However, according to such a molding method, it is difficult to mold such a material into a product having a complicated shape so that it has been practically impossible to correspond to cases where molded products having various shapes and dimensions depending upon individual remedies are required.
On the other hand, among hardenable materials for living body so far used, there are dental cement, dental composite resins, bone cement, etc.
These hardenable materials have been used in such a manner that they are in the form of paste or slurry at the time of their use, and after they have been filled in necessary parts in dental cavity or in vivo, they are hardened. Thus, these hardenable materials can be molded into an optimum shape depending upon individual remedies.
However, these conventional dental cement, composite resins, bone cement, etc. comprise components which are substances different from the hard tissue of living body, that is, inorganic and organic substances such as zinc oxide, silica powder, polyacrylate, eugenol, etc.; hence the conventional materials have defects of being difficultly operated in the aspect of stringiness or viscous properties. Further, the materials are fixed merely by a physical or chemical adhesion to living body; hence no assimilation with the tissue of living body occurs.
Thus, a method has been proposed which comprises filling a kneaded material in the form of slurry, composed mainly of a calcium phosphate convertible into apatite, in necessary parts in vivo or in the oral cavity, followed by hardening the material within a short time to form an apatite structure (Japanese patent application laid-open Nos. Sho 59-88351 and Sho 59-182263). According to the art disclosed in the laid-open gazettes, it is possible to form an apatite type hardened product at a temperature in the vicinity of that of living body within a relatively short time, by adding an organic or inorganic acid and an easily water-soluble halide to .alpha.-calcium triphosphate.
However, in order to practically use the apatite type hardened product obtained according to the above art, the following problems to be solved are left behind:
(1) The resulting hardened product has a hardness as low as about 6 kg/mm.sup.2 at the highest in terms of Knoop hardness.
(2) The hardened product has a very low stability in water and readily collapses.
(3) Its shrinkage at the time of hardening is so large that it is deficient in dimensional accuracy to make it difficult to adapt it to defect parts.